The present invention generally relates to bodily fluid sampling devices and more specifically, but not exclusively, concerns a bodily fluid sampling device configured to form an incision having a precise depth and express fluid from both finger and alternate site testing (AST) locations.
General Fluid Testing
The acquisition and testing of bodily fluids is useful for many purposes, and continues to grow in importance for use in medical diagnosis and treatment, and in other diverse applications. In the medical field, it is desirable for lay operators to perform tests routinely, quickly and reproducibly outside of a laboratory setting, with rapid results and a readout of the resulting test information. Testing can be performed on various bodily fluids, and for certain applications is particularly related to the testing of blood and/or interstitial fluid. Such fluids can be tested for a variety of characteristics of the fluid, or analytes contained in the fluid, in order to identify a medical condition, determine therapeutic responses, assess the progress of treatment, and the like.
General Test Steps
The testing of bodily fluids basically involves the steps of obtaining the fluid sample, transferring the sample to a test device, conducting a test on the fluid sample, and displaying the results. These steps are generally performed by a plurality of separate instruments or devices.
Acquiring—Vascular
One method of acquiring the fluid sample involves inserting a hollow needle or syringe into a vein or artery in order to withdraw a blood sample. However, such direct vascular blood sampling can have several limitations, including pain, infection, and hematoma and other bleeding complications. In addition, direct vascular blood sampling is not suitable for repeating on a routine basis, can be extremely difficult and is not advised for patients to perform on themselves.
Acquiring—Incising
The other common technique for collecting a bodily fluid sample is to form an incision in the skin to bring the fluid to the skin surface. A lancet, knife or other cutting instrument is used to form the incision in the skin. The resulting blood or interstitial fluid specimen is then collected in a small tube or other container, or is placed directly in contact with a test strip. The fingertip is frequently used as the fluid source because it is highly vascularized and therefore produces a good quantity of blood. However, the fingertip also has a large concentration of nerve endings, and lancing the fingertip can therefore be painful. Alternate sampling sites, such as the palm of the hand, forearm, earlobe and the like, may be useful for sampling, and are less painful. However, they also produce lesser amounts of blood. These alternate sites therefore are generally appropriate for use only for test systems requiring relatively small amounts of fluid, or if steps are taken to facilitate the expression of the bodily fluid from the incision site.
Various methods and systems for incising the skin are known in the art. Exemplary lancing devices are shown, for example, in U.S. Pat. Nos. Re 35,803, issued to Lange, et al. on May 19, 1998; U.S. Pat. No. 4,924,879, issued to O'Brien on May 15, 1990; U.S. Pat. No. 5,879,311, issued to Duchon et al. on Feb. 16, 1999; U.S. Pat. No. 5,857,983, issued to Douglas on Jan. 12, 1999; U.S. Pat. No. 6,183,489, issued to Douglas et al. on Feb. 6, 2001; U.S. Pat. No. 6,332,871, issued to Douglas et al. on Dec. 25, 2001; and U.S. Pat. No. 5,964,718, issued to Duchon et al. on Oct. 12, 1999. A representative commercial lancing device is the Accu-Chek Softclix lancet.
Expressing
Patients are frequently advised to urge fluid to the incision site, such as by applying pressure to the area surrounding the incision to milk or pump the fluid from the incision. Mechanical devices are also known to facilitate the expression of bodily fluid from an incision. Such devices are shown, for example, in U.S. Pat. Nos. 5,879,311, issued to Duchon et al. on Feb. 16, 1999; U.S. Pat. No. 5,857,983, issued to Douglas on Jan. 12, 1999; U.S. Pat. No. 6,183,489, issued to Douglas et al. on Feb. 6, 2001; U.S. Pat. No. 5,951,492, issued to Douglas et al. on Sep. 14, 1999; U.S. Pat. No. 5,951,493, issued to Douglas et al. on Sep. 14, 1999; U.S. Pat. No. 5,964,718, issued to Duchon et al. on Oct. 12, 1999; and U.S. Pat. No. 6,086,545, issued to Roe et al. on Jul. 11, 2000. A representative commercial product that promotes the expression of bodily fluid from an incision is the Amira AtLast blood glucose system.
Sampling
The acquisition of the produced bodily fluid, hereafter referred to as the “sampling” of the fluid, can take various forms. Once the fluid specimen comes to the skin surface at the incision, a sampling device is placed into contact with the fluid. Such devices may include, for example, systems in which a tube or test strip is either located adjacent the incision site prior to forming the incision, or is moved to the incision site shortly after the incision has been formed. A sampling tube may acquire the fluid by suction or by capillary action. Such sampling systems may include, for example, the systems shown in U.S. Pat. Nos. 6,048,352, issued to Douglas et al. on Apr. 11, 2000; U.S. Pat. No. 6,099,484, issued to Douglas et al. on Aug. 8, 2000; and U.S. Pat. No. 6,332,871, issued to Douglas et al. on Dec. 25, 2001. Examples of commercial sampling devices include the Roche Compact, Amira AtLast, Glucometer Elite and Therasense FreeStyle test strips.
Testing General
The bodily fluid sample may be analyzed for a variety of properties or components, as is well known in the art. For example, such analysis may be directed to hematocrit, blood glucose, coagulation, lead, iron, etc. Testing systems include such means as optical (e.g., reflectance, absorption, fluorescence, Raman, etc.), electrochemical, and magnetic means for analyzing the sampled fluid. Examples of such test systems include those in U.S. Pat. Nos. 5,824,491, issued to Priest et al. on Oct. 20, 1998; U.S. Pat. No. 5,962,215, issued to Douglas et al. on Oct. 5, 1999; and U.S. Pat. No. 5,776,719, issued to Douglas et al. on Jul. 7, 1998.
Typically, a test system takes advantage of a reaction between the bodily fluid to be tested and a reagent present in the test system. For example, an optical test strip will generally rely upon a color change, i.e., a change in the wavelength absorbed or reflected by dye formed by the reagent system used. See, e.g., U.S. Pat. Nos. 3,802,842; 4,061,468; and 4,490,465.
Blood Glucose
A common medical test is the measurement of blood glucose level. The glucose level can be determined directly by analysis of the blood, or indirectly by analysis of other fluids such as interstitial fluid. Diabetics are generally instructed to measure their blood glucose level several times a day, depending on the nature and severity of their diabetes. Based upon the observed pattern in the measured glucose levels, the patient and physician determine the appropriate level of insulin to be administered, also taking into account such issues as diet, exercise and other factors.
In testing for the presence of an analyte such as glucose in a bodily fluid, test systems are commonly used which take advantage of an oxidation/reduction reaction which occurs using an oxidase/peroxidase detection chemistry. The test reagent is exposed to a sample of the bodily fluid for a suitable period of time, and there is a color change if the analyte (glucose) is present.
Typically, the intensity of this change is proportional to the concentration of analyte in the sample. The color of the reagent is then compared to a known standard which enables one to determine the amount of analyte present in the sample. This determination can be made, for example, by a visual check or by an instrument, such as a reflectance spectrophotometer at a selected wavelength, or a blood glucose meter. Electrochemical and other systems are also well known for testing bodily fluids for properties on constituents.
Alternate Site Testing (AST)
As mentioned above, the fingertip is frequently used as the fluid source because it is highly vascularized and therefore produces a good quantity of blood. However, the fingertip also has a large concentration of nerve endings, and lancing the fingertip can therefore be painful. Alternate sampling sites, such as the palm of the hand, forearm, earlobe and the like, may be useful for sampling, and are less painful. However, they also produce less blood when lanced.
In general, bodily fluid sampling devices are designed to express blood from either the fingertip or an alternate site, but not both. Typically, alternate site sampling devices need to express fluid from a large surface area surrounding the site in order to draw a sufficient amount of fluid for testing. Furthermore, it is usually more desirable to lance the skin deeply at the alternate site in order to ensure that a sufficient amount of fluid can be expressed. In comparison, fingertips are relatively small and do not need to be deeply lanced or require a large area in order to express a sufficient amount of fluid. Therefore, alternate site sampling devices usually have larger openings for expressing fluid as compared to devices designed to express fluid from fingers. If an alternate site sampling device were used to lance and express fluid from a fingertip, severe pain or serious injury to the finger may result. With the alternate site device, when an incision is being formed in the fingertip, the skin can tend to deform or bulge into the expression opening such that the lancet forms an incision with a greater depth than needed.
Thus, needs remain for further contributions in this area of technology.